Tris(5,6,7,8-tetrafluoronaphthalen-2-yl)borane, a Partially Fluorinated Boron Lewis Acid with Fluorination Distal to the Boron Atom

Typical congeners of the boron Lewis acid tris(pentafluorophenyl)borane, B(C6F5)(3), are fluorinated at the aryl groups directly attached to the boron atom. The chemistry of related electron-deficient boranes with fluorination distal to the Lewis acidic center is largely unexplored. The preparation and characterization of tris(5,6,7,8-tetrafluoronaphthalen-2-yl)borane are reported. It serves as a model system that provides sites for further substitution at C-1 and C-3 of the naphthalen-2-yl units. A Gutmann-Beckett analysis of its Lewis acidity revealed that, despite remote fluorination, it is as Lewis acidic as B(C6F5)(3). The new Lewis acid performs equally well in C=O and C=N reduction as well as dehydrogenative Si-O coupling involving Si-H bond activation. Adducts with water and a phosphine oxide are crystallographically characterized.